German patent publication 764103 describes the use of flat and curved impingement plates in the downcomer opening to limit the froth height in the downcomer. The publication is directed to so-called cross-over tray configurations for use in so-called foaming gas-liquid systems. FIG. 4 of this publication discloses an embodiment wherein three curved plates are placed in the downcomer opening. The tangent at the upper end of the illustrated plates form an angle with the horizontal of more than zero degrees.
When trying to increase the liquid and/or gas flows of the gas-liquid contacting columns as described above a maximum load will be observed. Higher loads will result in that the column fails to function as a liquid-gas contactor or separator due to a phenomena known as flooding. Flooding is described as excessive accumulation of liquid inside the column. The well known flooding mechanisms are downcomer back-up, jet flooding and downcomer choking. These mechanisms are described in Distillation Design, Henry Z. Kister, McGraw-Hill Inc., 1992, pages 267-291. According to this publication downcomer back-up is due to a build-up of liquid inside the downcomer causing the liquid to back-up on the tray leading to liquid accumulation on that tray. The liquid height in the downcomer is determined by the tray pressure drop, liquid height on the tray and frictional losses in the downcomer and downcomer slot area. Jet flooding or entrainment flooding is caused by a too high gas velocity leading to the entrainment of liquid, either by droplets or froth, to the tray above. The liquid will accumulate and leads to flooding. Downcomer choking is caused by a too high aerated liquid velocity in the downcomer. At a certain velocity the friction losses in the downcomer and downcomer entrance become excessive, and the frothy gas-liquid mixture cannot be transported to the tray below, causing liquid accumulation on the tray. With the term froth is to be understood any gas-liquid mixture present on the tray not depending on any flow regime.
The present invention aims to provide a gas-liquid contacting tray as described above which permits a higher gas and/or liquid loads. Thus a tray is aimed at having an improved capacity. This aim is achieved by the following tray.